Bridge unbalance indicating means



,-1 R. D. BURCHFIELD 4 L BRIDGE UNBALANCE INDICATING MEANS Filed Sept.20, 1946- iii 1:

EI 5. E.

Qvwwvlm Patented Dec. 2, 1947 BRIDGE UNBALANCE INDICATING MEANS Robert1)., Burchfield, Wllkinsburg, -Pa., assignor, by mesne assignments, tothe United States of America, as represented by the Atomic EnergyCommission Application September 20, 1946, Serial No. 698,337

be indicative of changes in potential of a direct current input signalaffecting an unbalanced condition of the bridge, the bridge circuitincluding a reflexed arrangement of a vacuum tube such that the vacuumtube performs dual functions as a controlled variable resistance directcurrent bridge leg and as an amplifier for the pulsating 6 Claims. (Cl.177-311) current output signal resulting upon the unbalanced conditionof the bridge circuit.

The bridge circuit of this invention is of particular advantage whenconnected to the direct current output signal of a, Piram vacuum gaugeor an ionization vacuum gauge to provide for an audible indication of achange in pressure or vacuum conditions and hence provides for aneffective means of audible leak detection when checking large vacuumsystems for leaks.

Further objects and advantages of this invention will be apparent uponreferring to the following specification and drawing in which,

Fig. 1 is a schematic wiring diagram of the basic electrical bridgecircuit of this invention and,

Fig. 2 is a schematic wiring diagram of amodifled form of the electricalbridge circuit of Fig. 1 that is adapted to function from A. C. or D. C.live voltage power sources.

Referring to Fig. 1 of the drawings, the electrical bridge circuit IIIis comprised of the conjugate high resistance bridge legs I I, I2, thevariable resistance l3 in series with the high impedance magnetic typeearphones l4 and the triode vac- The direct current signal input whosechanges' in potential are to be audibly indicated by the bridge circuitof this invention is applied to the signal input terminals and 25,terminal 25 being connected to the negative bridge terminal I8 nectedthrough the secondary 26 of transformer 23 to the grid electrode 21 oftube l5. It will be noted that the plate 28 of tube i is connectedthrough the earphones I4 and variable resistance l3 to the positivebridge terminal ll while the of the bridge circuit while terminal 24 isconcathode 29 is connected to the negative terminal nal input terminals24 and 25 to provide a grid return for the grid-cathode circuit of tubeIS.

The operation of the invention as described in connection with Fig. 1 ofthe drawings is as follows: The bridge circuit I0 is first adjusted to apredetermined condition of balance by suitably adjusting the variableresistance Hi. The predetermined condition of balance may be such as tocause no current flow between the bridge terminals l9 and 20 or it maybe such as to cause a predetermined potential-difference betweenterminals l9 and 20, as desired. In any event, a change in the conditionof balance for the bridge circuit will change the potential differencebetween terminals l9 and 20 with respect to the potential difference forthe predetermined condition of bridge balance. As is well known, thefrequency of response for the interrupter 2| will be proportional to thepotential difference of the applied direct current and hence thefrequency will vary with a change in condition of balance for the bridgecircuit. The direct current signal whose potential change is to beindicated by a changein balance of the bridge circuit I0 is appliedthrough the input terminals 24 and 25 and the secondary 26 oftransformer 23 to the grid of tube l5. Thus a change in D. C. inputsignal will change the potential on grid 21 of tube l5 thus changingthat tubes internal resistance and the condition of balance for thebridge. This changed condition of balanceeauses a change in thefrequency of the pulsating current passing through the primary winding22 of transformer 23 between the bridge output terminals I9 and 20.

The pulsating current in the primary winding 22 induces a similarpulsating current in the transformed secondary winding 25 which is alsoapplied to the grid 21 of triode l5 causing amplifled pulsations ofsimilar frequency to appear in the tube plate load comprised ofheadphones [4 together with the adjustable resistance l3 and tocirculate in the bridge circuit. If the interrupter 2| is of the audiblefrequency buzzer type, the pulsations will be of an audible frequencyand therefore an audible indication of change in frequency due to changein the D. .0. signal input to terminals 24 and 25 will be heard in theearphones l4. It is to be noted that in the circuit of this invention.the triode I5 is used in a reflex manner to function as a variableresistance direct current leg of the bridge circuit "and as an amplifierfor the pulsating bridge output current in the primary 22 of transformer23.

The circuit of Fig. 2. is similar to that of Fig. 1 except that a dualpurpose tube 60 which may be a dual triode is used. One section of thedual purpose tube-ill is connected as a rectifier to pronection to a 110volt A. C. or D. C. line voltage source. Plate SI and grid 82 areconnected together and to terminal 42-whiie the cathode 63 is connectedthrough a filter condenser 64 to terminal 4| thus providing a half waverectifier circuit. The rectifier output appearing between the cathode 63and terminal 4| is applied to the bridge circuit 40 in the same manneras the bate tery i6 is connected to the bridge circuti IQ of Fig. 1. Thebridge circuit of Fig. 2 is in all other respects identical to thebridge circuit of Fig. 1 except for the provision of a cathode biasresistance 43 to obtain proper bias conditions for the triode sectioncomprised of plate 44, grid 45 and cathode 46.

The operation of the electrical bridge circuit 40 is identical with thatdescribed for bridge circuit l shown in Fig. 1 except that terminals 4|and 42 are properly polarized and connected to an A. C. or D. C. sourceof line voltage in place of the battery l6.

It will perhaps be noted that a description of the filament connectionsfortubes l5 and 60 has been omitted but since such connections are wellknown it is thought unnecessary to refer to them in detail. It shouldalso be understood that the tube types or circuit values which may beused in the bridge circuit of this invention are not critical to itsproper functioning within thepurview of the invention.

I claim:

1. Electrical circuit means for providing a pulsating current frequencychange indicative of a change in potential of a direct current signal,said circuit comprising a direct current resistance bridge, a resistanceleg of said bridge being comprised of a vacuum tube having a controlgrid, cathode and plate; another leg of said bridge including means toindicate the frequency of any pulsating current circulating in saidbridge, a direct current power source connected to the input terminalsof said bridge, an interrupter connected in series with a primarywinding of a transformer across the output terminals of said bridge, anda secondary winding of said transformer connected in series with thedirect current input signal to be indicated and the grid-cathode changein potential of a direct current signal, said circuit comprising adirect current resistance bridge, a resistance leg of said bridge beingcomprised of a vacuum tube having a control grid, cathode and plate;another leg of said bridge including means to'indicate the frequency ofany pulsating current circulating in said bridge, a direct current powersource connected to the input terminals of said bridge, adjustable meansto balance said bridge, an interrupter connected in series with aprimary winding of a transformer across the output terminals of saidbridge, and a secondary winding of said transformer connected in serieswith the direct current input signal to be indicatedand the grid-cathodecircuit of said vacuum tube.

3. Electrical circuit means for providing an audible pulsating currentfrequency change indicative of a change in potential of a direct currentsignal, said circuit comprising a direct current resistance bridge, aresistance leg of said bridge being comprised of a vacuum tube having acontrol grid, cathode and plate; another leg ofsaid bridge includingmagnetic earphones to indicate the audible frequency of any pulsatingcurrent circulating in said bridge, a direct current power sourceconnected to the input terminals of said bridge, an interrupterconnected in series with a primary winding of a transformer across theoutput terminals of said bridge, and a, secondary winding of saidtransformer connected in series with the direct current input signal tobe indicated and the grid-cathode circuit of said vacuum tube.

4. Electrical circuit means for providing an audible pulsating currentfrequency change indicative of a change in potential of a direct currentsignal, said circuit comprising a direct current resistance bridge, aresistance leg of said bridge being comprised of a vacuum tube having acontrol grid, cathode and plate; the conjugate bridge leg connected tothe plate of said vacuum .tube including a pair of magnetic earphones toindicate the audible frequency of any pulsating current circulating insaid bridge, a direct current power source connected to the inputterminals of said bridge, an interrupter connected in series with aprimary winding of a transformer across the output terminals of saidbridge, and a secondary winding of said transformer connected in serieswith the direct current input signal to be indicated and thegrid-cathode circuit of said vacuum tube.

5. Electrical circuit means for providing. an audible pulsating currentfrequency change indicative of a change in potential of a direct our--rentsignal, said circuit comprising a direct current resistance bridge,a resistance leg of said bridge being comprised of a vacuum tubehaving acontrol grid, cathode and plate; another leg of said bridge includingmagnetic earphones to indicate the audible frequency of a pulsatingcurrentcirculating in said bridge, a direct current power sourceconnected to the input terminals of said bridge, adjustable means. tobalance said bridge, an-interrupter connected in series with a primarywinding of a transformer across the output terminals of said'bridge, anda secondary winding of said transformer connected in series with thedirect current input signal to be indicated and the grid-cathode circuitof said vacuum tube.

6. Electrical circuit means for providing an audible pulsating currentfrequency change indicative of a change in potential of a direct currentsignal, said circuit comprising a direct current resistance bridge, aresistance leg of said bridge being comprised of a vacuum tube having acontrol grid, cathode and plate; the conjugate bridge leg connected tothe plate of said vacuum tube including a pair of magnetic earphones toindicate the audible frequency of any pulsating current circulating insaid bridge, a direct cur- ,rent power source connected to the inputterminals of said bridge, adjustable means to balance said bridge, aninterrupter connected in series with a primary winding of a transformeracross. the output terminals of said bridge, and a sec--- ondary windingof said transformer connected in series with the direct current inputsignal to be indicated and thelgrid-c'athode circuit of said vacuumtube.

' ROBERT D. BURCHFIELD.

